1. Field of the Invention
The present invention relates to a zoom lens barrel and more precisely it relates to a zoom lens barrel in which the back focal distance (back focus) can be easily adjusted. The present invention also relates to a method for adjusting the back focal distance using the zoom lens barrel.
2. Description of the Related Art
In a zoom lens barrel, it is necessary to carry out the zoom adjustment and back focus adjustment upon assembly of the same. The zoom adjustment is effected to make the focal position at the short focal length extremity and the focal position at the long focal length extremity identical. In a two-lens group type zoom lens, the zoom adjustment is executed by varying the distance between a first lens group and a second lens group. In the back focus adjustment, the entirety of the lens system is moved in the optical axis direction without varying the distance between the first and second lens groups to make the focal position coincident with the rail surface (film surface) of the camera.
In conventional zoom lens barrels, the zoom adjustment and the back focus adjustment are mechanically effected by means of complicated adjusting mechanisms, thus resulting in a large camera.